Insights into sperm–fertilisation relationships in the Arthropoda with ecological significance modelled in an amphipod

Evaluation of precopulatory pairing behaviour and male fertility in a marine amphipod exposed to plastic additives

Plastics contain a mixture of chemical additives that can leach into the environment and potentially cause harmful effects on reproduction and the endocrine system. Two of these chemicals, N-butyl benzenesulfonamide (NBBS) and triphenyl phosphate (TPHP), are among the top 30 organic chemicals detected in surface and groundwater and are currently placed on international watchlist for evaluation. Although bans have been placed on legacy pollutants such as diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP), their persistence remains a concern. This study aimed to examine the impact of plastic additives, including NBBS, TPHP, DBP, and DEHP, on the reproductive behaviour and male fertility of the marine amphipod Echinogammarus marinus. Twenty precopulatory pairs of E. marinus were exposed to varying concentrations of the four test chemicals to assess their pairing behaviour. A high-throughput methodology was developed and optimised to record the contact time and re-pair time within 15 min and additional point observations for 96 h. The study found that low levels of NBBS, TPHP, and DEHP prolonged the contact and re-pairing time of amphipods and the proportion of pairs reduced drastically with re-pairing success ranging from 75% to 100% in the control group and 0%-85% in the exposed groups at 96 h. Sperm count declined by 40% and 60% in the 50 μg/l and 500 μg/l DBP groups, respectively, whereas TPHP resulted in significantly lower sperms in 50 μg/l exposed group. Animals exposed to NBBS and DEHP showed high interindividual variability in all exposed groups. Overall, this study provides evidence that plastic additives can disrupt the reproductive mechanisms and sperm counts of amphipods at environmentally relevant concentrations. Our research also demonstrated the usefulness of the precopulatory pairing mechanism as a sensitive endpoint in ecotoxicity assessments to proactively mitigate population-level effects in the aquatic environment.

Unusual male size vs sperm count relationships in a coastal marine amphipod indicate reproductive impairment by unknown toxicants

Sperm quantity/quality are significant reproductive endpoints with clear links to population level dynamics. Amphipods are important model organisms in environmental toxicology. Despite this, field monitoring of male fertility in invertebrates has rarely been used in monitoring programs. The aim of this study was to compare sperm quality/quantity in an amphipod collected at six UK locations with differing water quality. Due to low sperm counts and an observed lack of relationship between sperm count and weight in amphipods collected from a nationally protected conservation area (Langstone Harbour, England), we also compared datasets from this site over a decade to determine the temporal significance of this finding. One collection to evaluate a female reproductive endpoint was also performed at this site. Interestingly, this harbour consistently presented some of the lowest sperm counts comparable to highly industrial sites and low eggs number from females. Amphipods collected from all the sites, except from Langstone Harbour, presented strong positive correlations between sperm count and weight. Given Langstone Harbour has several international and national protected statutes primarily for marine life and birds, our results indicate that E. marinus, one important food component for wading birds, might be impacted by unknown reproductive stressors. These unknown stressors maybe related to agricultural runoff, leachate from historical landfills and effluent from storm water overflows. This study highlights the importance of exploring new reproductive endpoints such as sperm quantity/quality in marine monitoring programs.

Impacts of ionising radiation on sperm quality, DNA integrity and post-fertilisation development in marine and freshwater crustaceans

Crustaceans have been designated as internationally important model organisms in the development of environmental radioprotection measures. Despite the known sensitivity of sperm to ionizing radiation, the impacts of chronic radiation exposure on male fertility in crustaceans have not been studied. For the first time, the present study aimed to assess the impacts of chronic radiation exposure on male fertility, sperm DNA damage and concomitant impacts on breeding in two amphipod crustaceans. Echinogammarus marinus and Gammarus pulex (male fertility only) were exposed to phosphorus-32 at dose rates of 0, 0.1, 1 and 10 mGy/d and sperm parameters, DNA damage and knock-on impacts on breeding were assessed. Sperm quality parameters and DNA damage were assessed using a fluorescent staining method and single cell gel electrophoresis respectively. Concomitant effects of male exposure to radiation on fecundity were determined by pairing phosphorus-32 exposed males to unexposed sexually mature females. In E. marinus, a statistically significant reduction of 9 and 11% in the quality of sperm was recorded at dose rates of 1 and 10 mGy/d respectively, with no significant effects recorded on sperm counts. Conversely in the freshwater G. pulex, no significant impact of radiation on sperm quantity or quality was recorded. For E. marinus, a statistically significant increase in DNA damage was recorded at doses of 10 mGy/d. Reduced fecundity and an increase in the frequency of abnormal embryos was recorded in female E. marinus breeding with males exposed to radiation. These findings suggest sperm quality may be a sensitive indicator of radiation exposure in invertebrates with potential impacts on the unexposed embryo, though unclear dose-response and differences between two closely related species necessitate further study before robust conclusions can be drawn.

Effects of cyproterone acetate and vertically transmitted microsporidia parasite on Gammarus pulex sperm production

Endocrine disruption compounds (EDCs) and parasitism can both interfere with the reproduction process of organisms. The amphipod Gammarus pulex is the host of the vertically transmitted microsporidia Dictyocoela duebenum, and this work was devoted to the investigation of the effect of an exposure to the anti-androgen compound, cyproterone acetate (CPA), and/or of the presence of D. duebenum on the spermatozoa production and length. Significant reduction of the spermatozoa production was observed when G. pulex males were uninfected and exposed to CPA. There also appeared a lower number of spermatozoa when D. duebenum infects G. pulex, whatever the exposure condition. Moreover, we highlighted that CPA has no effect on spermatozoa production when males are infected by D. duebenum, and no treatment has impacted the spermatozoa length. Our results suggest CPA and D. duebenum could impact the endocrine system of G. pulex and especially processes close to the spermatozoa production (e.g., androgenic gland, androgen gland hormone released, gonad-inhibiting hormone synthesized by X-organ). However, as no mechanism of action was highlighted, further testing need to be performed to improve the understanding of their impacts. Finally, results confirm that vertically transmitted microsporidia could be a confounding factor in the endocrine disruption assessments in Gammaridae.

Infertility in male aquatic invertebrates: a review

As a result of endocrine disruptor studies, there are numerous examples of male related reproductive abnormalities observed in vertebrates. Contrastingly, within the invertebrates there have been considerably less examples both from laboratory and field investigations. This has in part been due to a focus of female related endpoints, inadequate biomarkers and the low number of studies. Whether contaminant induced male infertility is an issue within aquatic invertebrates and their wider communities therefore remains largely unknown and represents a key knowledge gap in our understanding of pollutant impacts in aquatic wildlife. This paper reviews the current knowledge regarding pollutants impacting male infertility across several aquatic invertebrate phyla; which biomarkers are currently being used and where the science needs to be expanded. The limited studies conducted so far have revealed reductions in sperm numbers, examples of poor fertilisation success, DNA damage to spermatozoa and inhibition of sperm motility that can be induced by a range of environmental contaminants. This limited data is mainly comprised from laboratory studies with only a few studies of sperm toxicity in natural populations. Clearly, there is a need for further studies in this area, to include both laboratory and field studies from clean and reference sites, with a focus on broadcast spawners and those with direct fertilisation. Biomarkers developed for measuring sperm quantity and quality in vertebrates are easily transferable to invertebrates but require optimisation for particular species. We discuss how sperm tracking and techniques for measuring DNA strand breaks and sperm viability have been successfully transferred from human infertility clinics to aquatic invertebrate ecotoxicology. Linking sperm toxicity and male infertility effects to higher level impacts on the reproductive biology and dynamics of populations requires a much greater understanding of fertilisation dynamics and sperm competition/limitation for invertebrate species and represents the next challenge in our understanding of male toxicity effects in natural populations.